Aerospace sheet metal manufacturing MES solution


MES system overview
MES was proposed by Main AMR in the 1990s. The definition of MES by MESA (MES International Federation) is: "MES can optimize the entire product production process from the beginning of the order to the completion of the product through the transmission of information. The management, timely response and report to real-time incidents occurring in the factory, and use the current accurate data for corresponding guidance and processing". MES is a production management technology and real-time information system oriented to the inter-vehicle level. It is a basic technical means to implement agile manufacturing strategy of enterprises and realize agile production in the workshop.

Characteristics of sheet metal manufacturing workshop
Before the Boeing 787, sheet metal parts accounted for about 70% of the aircraft body structure, and the number of tooling and total working hours accounted for about 60% and 25%, respectively. Boeing has adopted a large number of new materials and new processes in the design of the Boeing 787 aircraft, which has greatly reduced the number of sheet metal structural parts of the aircraft, but the number of sheet metal parts still accounts for more than 50% of the aircraft structural parts. The production characteristics of the sheet metal workshop are as follows.

1 Complex production process
The production of sheet metal parts involves both machining process and special process, both conventional quality inspection and special process inspection. The process flow involves both single-piece production and batch production.

2 Short production process cycle
Compared with machined parts, the production cycle of sheet metal parts is very short. Except for the heat table process, other processes are basically calculated in minutes.

3 Complicated planning
The short production cycle of sheet metal parts determines the short planning cycle and high planning frequency; the coexistence of single piece flow and batch production determines the complexity of the planning mode. When planning, not only resource capacity must be considered, but also task priority and single piece Coordination between production plan and batch production plan.

4 high manufacturing cost
The value of the process equipment used in the production of sheet metal parts is very high. If the process plan is not coordinated before and after, there will be waiting during the heat meter process, the equipment utilization rate is not high, the capacity utilization is insufficient, and the cost per unit product to be shared is higher. In addition to the consumables and management costs required for manufacturing record printing, the management cost of small sheet metal parts will be much higher than the direct cost.

MES overall structure of sheet metal workshop
From the above analysis, it can be seen that the production of sheet metal parts has the characteristics of difficulty in planning, short planning cycle, multiple planning objects, conflicts of key production resources, coexistence of single piece flow and batch production, and high manufacturing costs.

The overall goal of Shenfei Civil Aircraft Company's production management and control system is to realize the intelligent and information management of related businesses in the production and management of the sheet metal workshop surrounding China. With planning and scheduling as the core, Kanban as the pull, and the information push mechanism as the starting point, an efficient coordinated action mechanism between management personnel, technicians and workers has been established. The overall system architecture is shown in Figure 1.

The system is driven by the production orders generated by the ERP system and the process flow data of the CAPP system, and realizes the management of the production process through the simulation of production scheduling, the release of production scheduling, production dispatch, and schedule and quality information collection. Combined with the use of the office system, a cross-system based on-site problem reminding and handling mechanism based on process integration is established. The implementation of the system needs to be resolved: how to achieve efficient operation planning, how to quickly implement process changes, how to establish a practical production kanban system, and how to implement key technologies such as integration with ERP, CAPP, and office systems.

Research on Process Improvement and Optimization Scheme
The technological process is the basis for planning, scheduling, dispatching, and progress feedback. When the craftsmen of Shenfei Civil Aircraft Company did not consider the requirements of paperlessness and lack of information flow, the craftsmanship has the following problems: the crafting route is cumbersome, leading to frequent reports; crafting changes need to be made in different software systems Repeated operations; need to manually implement emergency changes on production orders; lack of available resource information and man-hour information in the process; faced with a large amount of data, planners and team leaders cannot quickly merge hot table processes; there is no ability data for process merging Support etc. In response to the above problems, the following improvement measures are proposed.

1 Reduce the number of processes and inspection points
Sort out the unreasonable setting of procedures and unreasonable setting of inspection points. Change the process preparation method and improve the process flow from the quality system and process system.

2 Supplement necessary process information
Copy the finalized process information from the process system CAPP to the MES system, supplement information such as working hours, equipment group, etc., establish a process specification upgrade inspection and process data integrity check mechanism to ensure the consistency of the data in the CAPP system and the MES system And completeness.

3 Establish a process feature code that guides process merging
Comprehensive consideration of factors such as project (or model), material grade, incoming state, final state, material classification, heat treatment method, material thickness, etc., a process feature code is established in the MES system, and each part is assigned a feature code. During business operations, relevant personnel no longer need to check the process specifications, drawings and manuals. As long as the feature codes in the system are the same, it means that the parts can be processed at the same time. Faced with a large amount of business data in the MES system, operators are no longer confused or at a loss. Table 1 is an example of process feature code coding.

4 Establish the capability model of the equipment
Most of the hot surface treatment equipment has volume or surface area limitations. Even with the process feature code, the relevant personnel cannot know how many parts can be processed at a time from the data in the MES system, and the user will also be confused when operating. Let's take the quenching furnace as an example to illustrate the method of establishing the capacity model.

In Table 2, the processing batch size is adjusted according to the production strategy, that is, the planned number of production orders in the ERP; the available production volume is: how many pieces can be processed at a time when only processing the same part, this data is given by the heat meter technician The calculation method of batch capacity requirement is: batch capacity requirement=processing batch×total equipment capacity/production capacity.

In order to make the calculated data look regular, the total capacity of the equipment can be 100, 1000 or 10000 as the base, and the calculation result can take different decimal places. When planners and team leaders make planning decisions and production decisions, the system will perform a first-level sorting according to the process feature code, and a second-level sorting according to the order arrival time, and automatically calculate the capacity requirements. When the cumulative capacity is greater than the equipment capacity, The system starts from the current order and then calculates the accumulation of equipment capacity data.

5 Develop a change implementation process
As shown in Figure 2, when engineering or process changes occur, the craftsman upgrades the process specification in CAPP, and then enters the MES system to guide the new version of the process. If the technologist forgets to guide the new version of the process, the planner can automatically check whether there is an upgrade of the process specification through the program during production scheduling, and automatically download and update if there is; if the order is in an unplanned state, the system will notify the plan when the change is implemented If the order is planned or in production, the technician will use the emergency implementation function to display the order that needs to be urgently implemented on the screen in the form of a list, and the system will also prompt the process number of the order that has been processed. In the list, select the order number that needs to be changed and implemented immediately, the system will automatically copy the new version of the process route to the selected order, but it is not allowed to re-copy the process information to the completed or in-production process, the system can quickly complete Urgent implementation of a large number of process changes during the development phase.

APS Planning and Scheduling Strategy
APS is the core function of the MES system, which mainly solves the limited capacity scheduling problem that MRP cannot do. However, in view of the characteristics of the sheet metal workshop, the monthly planning objects range from hundreds to thousands of parts, and there are coordination problems between single-piece production and batch production. The planner's planning and scheduling strategies and methods are as follows.

1 Establish a linkage mechanism for assembly missing parts demand
The driving data of the MES system comes from the ERP parts production order, which is the planned demand generated by the inversion of the assembly process demand time. This demand has comprehensively considered the parts inventory and the production orders that have been placed, as well as the priority of the demand time, and realized the demand linkage with the ERP system.

Once there is an emergency missing part on the production line in the assembly workshop, the assembly MES system will automatically transmit the missing part information to the MES system of the parts workshop, and make color markings on the orders of the corresponding parts in the MES system of the parts workshop, so that the part planner and related personnel can understand in time The urgent needs of the assembly workshop facilitate the planning and arrangement of the parts car planners prioritized, and the linkage processing of missing parts information in the assembly workshop and the parts workshop has been realized.

2 Establish a production scheduling strategy based on priority planning.
In the event of resource conflicts, planners can use priority definitions to prioritize production of orders with high priority.

3 Establish a pre-scheduled work mechanism
What APS provides is a fast calculation tool for complex calculation models with large amounts of data, which cannot be done manually. However, APS cannot replace manual decision-making, nor can it complete the preparation of the operation plan through a single schedule.

Step 1: The planner first pre-schedules the production according to the selected plan object. At this time, high priority orders and urgent missing parts orders have been considered.
Step 2: The planner merges the processes according to the expected arrival time of the parts in the first mergeable process, whether they can be processed in parallel, and the equipment capacity requirements, etc.
Step 3: The planner pre-schedules production according to the merged data.
Step 4: Repeat steps 3 and 4 until all the combinable processes have been processed.

4 Develop a planning and decision-making mechanism for processes that can be combined
The MES system will perform a first-level sorting according to the process feature code, and a second-level sorting according to the time to reach the mergeable process. At the same time, the equipment capacity occupancy accumulation calculation is performed according to the equipment capacity. When the demand capacity exceeds the equipment capacity, the capacity demand accumulation is performed again . Planners can make decisions based on the data provided by the system.

5 Establish an adjustment mechanism for the operation plan
After the operation plan is issued, due to many accidents in the on-site production, the parts may not arrive at the mergeable processing station according to the pre-arranged schedule. If there is no merged process adjustment mechanism, it will inevitably cause production waits and idle equipment. When dispatching work, the team leader of the mergeable process can adjust the merged process block to meet the actual needs of on-site management. The processing of the adjustment data is consistent with the content of the above-mentioned "Merging Process Planning Decision Mechanism". It is possible to adjust the part orders that have not arrived from the process block, or adjust the part orders that have arrived at the merge station but have not been included in the merge process to the process block.

Kanban design
Kanban mainly plays a role in pulling on-site management and control. According to the role of Kanban, in the MES system of Shenfei Civil Aircraft, Kanban is divided into 4 categories, namely, progress, missing parts, problem, and equipment. The following is one for progress and one for missing parts to illustrate the design ideas and contents of the display.

1 Production task backlog Kanban
(l) Kanban design purpose: managers can grasp the macro situation of the progress of each team's production tasks, the rationality of task allocation, capacity utilization, and whether the production line capacity is balanced, so that the production control personnel can schedule in time, balance resources, and provide production line balance. Basis for decision-making.

(2) The content displayed by the kanban: the number of orders that have arrived in the team but have not yet started, as shown in Figure 3.

2Emergency missing parts board
(1) Kanban design purpose: Relevant personnel can grasp the urgent needs of the assembly workshop at any time, so as to timely plan, schedule, produce, transport, receive, and issue, so as to meet the needs of the assembly workshop as soon as possible and improve customer satisfaction.
(2) The objects of Kanban concern are managers, planners, dispatchers, team leaders, logistics supervisors, and warehouse managers.
(3) The content displayed on the kanban board is the missing parts list issued by the MES system of the assembly workshop, which is processed by the ERP and MES system of the parts workshop to associate the demand factory, project, material number, drawing number, quantity, supply factory, status and other information, as shown in the table 3 shown.

In addition to displaying the above-mentioned related information on the large screen, the missing parts information sent by the MES of the assembly workshop will automatically mark the relevant parts orders in the parts car MES system with special colors, and relevant personnel can quickly get the missing parts information from the system. Planners raise the priority of orders in a timely manner, team leaders give priority to orders, logistics personnel individually package and transport missing parts with drawing numbers, and Kuzhu staff in time prioritize accounts in the ERP system and send materials to the assembly workshop.

The missing parts kanban uses a fixed number of lines to scroll and display. When there is no missing parts, it will not be displayed. After the missing parts are processed, the missing parts information will not be displayed.

system integration
The MES system of the sheet metal workshop of Shen Fei Civil Aircraft Co., Ltd. aims at paperless manufacturing records, takes the process flow of sheet metal parts as the main line, and takes APS scheduling as the core. Establish a set of production workshop management and control platform. The platform is based on the process data of the CAPP system, driven by the production order data of the ERP system, and relying on the process of the administrative office system to realize fully digital vehicle management. The integration relationship is shown in Figure 4.

It can be seen from the figure that the MES system receives production orders from the ERP system and obtains the process flow of the parts from the CAPP system. At the same time, it is necessary to consider whether there is a new version of the process specification in the CAPP. If there is a new version of the process specification, Then carry out APS production scheduling, after the plan is released, dispatch workers in teams.

If it is a blanking process, after the completion of the job, in addition to the job report, the material backflushing consumption must be carried out in the ERP system; during the process operation, if there is an emergency change, the technician will update the process specification in the CAPP system, and then use the MES The system changes and implements the orders in production.

Since the process processing of the MES system itself can enable personnel to initiate a rejection report from the MES system, the report number is automatically associated with the manufacturing record, and the approval process of the rejection report in the OA system is triggered at the same time. After the answer, it will be reworked/repaired, scrapped, and original Use the three situations to deal with separately. If it is scrapped, you need to directly trigger the scrapping process from the OA for approval. If it is rework/repair, you need to sub-card the order. When reporting work, consider the association of the order. ERP transmits information such as qualified quantity, scrap quantity, and whether part of the job is reported.

After the final inspection, the MES system automatically triggers the order receipt in the ERP system, and the parts are received to be handed over to the warehouse. The logistics personnel hand over the report in the MES system according to the type and address of the handover warehouse. After the material custodian checks and confirms, it is automatically triggered The materials in the ERP system are moved to the delivery factory.

1 Integration with ERP and OA systems
The SAP ERP system has many open interface methods, including direct and indirect methods, but limited to the interface method of the MES system, the intermediate database interface method is used to realize the integration of the two systems. In ERP and OA, the WVERSERVICE interface program is compiled through JAVA language, and different data requests are monitored through different port numbers, including different services such as downloading of orders, job reporting, human database, database transfer, approval circulation, etc. The integration method is shown in Figure 5. Show.

2 Integration with CAPP system
     The CAPP system does not use open interface programs. When integrating with the MES system, the direct integration method is adopted, that is, the underlying database of the CAPP system is directly accessed in the MES system to realize data exchange.
Concluding remarks
     This paper analyzes the production characteristics of aviation sheet metal parts, and the current status of informatization of Shen Fei's civilian aircraft, combined with the implementation experience of the MES system, and summarizes several key technologies encountered during the implementation of the MES system in the sheet metal workshop and their processing methods and methods. There are many key technologies that are not covered in this article, such as how to achieve paperless manufacturing records and pass the quality system certification, how to reflect the needs of MBD in the workshop on-site management and control system, etc. These technologies need to be further studied.